The hum appeared right after fitting different wheels. What is it?

Almost certainly the tyres: a different tread pattern, a different compound, or uneven wear on the old set. A bearing cannot switch on that abruptly — its hum builds week by week. To check, refit the previous set or swap the wheels around.

What is sawtooth wear and why does it hum?

It is stepped wear of the tread blocks, where each block wears more on one side. Those steps strike the road thousands of times a minute and produce an even hum very like a bearing. Check it with your palm: run it across the tread along the axis of rotation — a sawtooth tyre feels like a grater.

Does the coasting test work?

Only halfway. Coasting in neutral rules out the engine and gearbox: if the hum stays, its source rotates with the wheels. But both a bearing and a tyre rotate with the wheels, so this test cannot separate them — you need the surface, cornering and wheel-swap tests.

Winter tyres hum on tarmac. Is that normal?

Yes. A soft compound, deep sipes and especially studs are noticeably noisier than a summer set, and hum on clean tarmac is normal rather than a fault. What should concern you is different: if the same set has become noticeably louder than last season, or changed in corners, check the bearings and the tread wear.

Hum: wheel bearing or tyres — how to tell

A low hum at speed is one of the most common complaints at a workshop and one of the most deceptive: a worn wheel bearing — the part the wheel turns on — and noisy tyres sound so alike that experienced mechanics get it wrong. The cost of the error runs in both directions: you can replace a healthy bearing and keep the hum, or blame the tyres for months while the bearing develops play. Here is how these sounds differ and how to separate them in a single drive.

Why they get confused

The main thing is the same in both: a low-frequency hum that grows with road speed and ignores engine revs. Coasting in neutral removes neither — in both cases the source rotates with the wheel. So the classic “press the clutch and listen” trick is useless here: it rules out the engine and the gearbox, not the two main suspects.

They have to be told apart by indirect signs: the reaction to the road surface, behaviour in corners, the history of the sound and the wear pattern on the tread. No single sign is a verdict, but three or four matches usually give a confident answer.

Side by side

Sign	Wheel bearing	Tyres
Reaction to the surface	Almost the same on any tarmac	Noticeably quieter on fresh smooth tarmac
Gentle corners at 60–80 km/h	Louder one way, quieter the other	Practically unchanged
Character of the sound	Even hum, later a rumble and howl	Grainy rolling noise; when worn, hum with a beat
How it appeared	Gradually, building over weeks	Right after a wheel change, or with tread wear
Seasonality	Independent of season	Winter and off-road treads are noisier by design
Vibration	At a late stage, in the wheel and floor	With uneven wear, a buzz at one speed
Swapping front and rear wheels	The hum stays where it was	The hum travels with the wheels

Three tests in one drive

The surface test. Drive one route over different tarmac: fresh and smooth, then coarse and old. Almost no change points at the bearing; a noticeable drop on the smooth stretch points at the tyres. Mind the trap: a tyre with severe sawtooth wear hums on any surface, so this test alone does not decide it.
The cornering test. On an empty road at 60–80 km/h, ease left and then right. Weight moves to the outer wheels: if the hum grows when you ease left, the right-hand side is loaded and the right bearing is the suspect, and vice versa. Tyre noise barely changes during gentle lane changes.
The swap test. The most honest of the home tests: swap the front and rear wheels. If the hum moves from one axle to the other, the tyres are guilty; if it stays put, they are not.

An extra clue is history. A hum that appeared on the day of a tyre change is almost always about the wheels: a different set, a different pattern, fitting errors. A hum that was barely audible a month ago and is now obvious to passengers is the typical trajectory of a bearing.

When the tyres are humming: the typical cases

Sawtooth wear. Tread blocks wear in steps — more often on the rear axle and on tyres that have not been rotated for a long time. It gives an even low hum, maximally similar to a bearing.
Uneven wear from alignment or pressure. Eaten inner or outer shoulders, patches from running out of balance — hum plus light vibration.
Tread design. Winter sets, studs, off-road all-terrain and mud patterns are loud by construction, not by fault.
Hard or tired rubber. The compound hardens with age, and by its fifth season a once-quiet tyre gains a distinct voice.

The inspection takes a minute: run your palm across the tread along the axis of rotation, in both directions. If the surface feels stepped, like a grater, you have probably found the source.

A separate case is a directional tyre fitted against the rotation arrow, or an asymmetric one mounted with the “Inside” face outwards: such a set can hum straight after fitting. The Rotation arrow and the Outside/Inside markings on the sidewall take a minute to check with no tools.

When it is the bearing

Arguing for the bearing: the hum changing in gentle corners, the same sound on any surface, a gradual build over weeks, and the hum turning into a rumble. At later stages vibration and play join in: with the wheel raised you can feel a knock when rocking it vertically, and turning it by hand gives a rough, grainy resistance. On many cars a failed hub also triggers ABS fault codes, because the sensor is built into the hub.

What the repair involves

The workshop check is simple: the wheel is raised, rocked and spun while the mechanic listens to the hub — a few minutes, and often done at no charge when the repair is booked.

Two things decide the shape of the job. The first is whether your car uses a bearing that presses into the existing hub or a complete hub assembly replaced as a unit — that governs both the price and the time. The second is the hub nut torque: over- or under-tightening destroys a new bearing within thousands of kilometres, so a torque wrench rather than an impact gun is what you want to see.

If the tyres turn out to be the cause, the fix is usually cheaper, but the uneven wear itself deserves attention: it normally means alignment is out or the dampers are tired, and a new set on an unfixed car wears the same way.

The full tree of hum causes — not only bearings and tyres but the transmission too — is on the symptom pages humming while driving and wheel bearing hum.

And if you want a second opinion before the trip, record the hum while driving in the Pro-Stuk app: it analyses the recording, asks a few clarifying questions — about the surface, corners, how the sound appeared — and shows the likely causes with percentages.

Humming: wheel bearing or tyres — telling them apart